We are studying the motility of tumor cells as a component of metastasis. Our goal is to identify new proteins which play a role in tumor cell motility in an animal model system. We are conducting a mutation screen in which single-site mutations are generated in Drosophila which are lacking the tumor suppressor gene lethal giant larvae. Brain fragments from lethal giant larvae mutants are highly metastatic when transplanted into adult hosts. These new mutants can then be screened to identify mutations which cause either a suppression or enhancement of brain tumor cell motility. The mutations are being generated by mobilization of a genetically engineered single P element. We have screened over 10,000 flies for P element transposition and are recovering transformants at a frequency of 1.4%. The P element which is being used for mutagenesis was engineered to facilitate cloning of flanking DNA sequences. We have identified chemoattractants which stimulate motility in metastatic Drosophila cells and are testing our mutation lines for reduced or enhanced motility. This method will allow us to genetically analyze tumor cell motility and metastasis in the Drosophila model. In addition, we have tested specific mutations in components of the MAP kinase signal transduction cascade to determine if this signalling pathway is important in the metastasis of Drosophila tumors. Four novel genes have been identified which are functionally required for the phenotype of tumorigenicity and invasion. Two of these genes are required for invasion and metastasis, separate from tumorigenicity. One of these genes Semaphorin 5A encodes an extracellular protein with 7 thrombospondin repeats and mediates its function through the phosphorylation of SMAD in Drosophila and in the human neoplastic cells.